1. Field of the Invention
This invention relates to telephone subscriber loop range extenders and, more particularly, to a universal range extender applicable to any subscriber loop and particularly suited for concentrated range extension.
2. Description of the Prior Art
In order to provide for telephone service on very long subscriber loops, it is often necessary to provide voice frequency gain and supervisory signal detectors at the central office end of the subscriber loop. Such specialized facilities are called "range extenders with gain" (REGs). One such REG is shown in K. E. Stiefel U.S. Pat. No. 4,056,688, granted Nov. 1, 1977.
The need for a range extender on any particular subscriber loop is dependent on the length of that loop, normally specified by the resistance of the loop. Short loops, for example, do not require such range extension while very long loops cannot be serviced entirely from the central office end and usually require remote amplification. A range extender which is automatically adaptable to any length of loop is particularly desirable since the loop parameters then need not be investigated prior to installation. The aforementioned Stiefel patent discloses one such automatically adjusting range extender in which the gain of the voice frequency amplifier is varied as a function of the loop length. The Stiefel range extender, however, is not suitable for use with extremely long subscriber loops having remote amplification facilities.
Rather than providing a range extender for each subscriber loop in a telephone system, it is desirable to place the range extenders behind the first stage of the central office switch, thereby providing concentration of the subscriber loop traffic through the range extenders. Significantly fewer range extenders are required in this arrangement. One system showing such concentrated range extension facilities is found in K. F. Giesken U.S. Pat. No. 3,816,668, issued June 11, 1974. The present invention is a range extender particularly suitable for concentrated applications.